The present invention relates to an alarm apparatus, and more particularly to alarm apparatus for movable barrier members positioned in openings defined by frame members. For example, the alarm apparatus of the present invention is particularly useful as a burglar alarm for windows having venetian blinds or other types of shade or curtain type members which are movable in the window opening.
In prior art burglar alarm systems or alarm apparatus for windows and the like having flexible or movable barrier members, the alarms have been physically attached to the flexible movable barrier members and the barrier members in turn physically restricted or restrained from being freely movable relative to the window frame. Then, any movement of the barrier causes the alarm to be actuated. As can be appreciated, such an arrangement hampers normal use of the barrier member and/or requires complicated hardware or apparatus for holding the barriers fixed in the window openings. Further, the restraining apparatus such as locks, hooks, etc. has resulted in an unslightly and non-aesthetic appearance for the barrier members mounted in the openings. Consequently, such prior art alarm systems for blinds or flexible barrier members have not been widely used in the past.
For example, in U.S. Pat. Nos. 2,287,382 and 2,293,609, both to Livingston, for "Barrier Alarms", there is disclosed alarm apparatus for venetian blind type barriers or the like in which the blind is held in fixed position with respect to the window frame by means of bolts or studs attached to the blinds and hook members attached to the window frame. The studs are disposed in a non-contact relationship within the hook members, and an electrical circuit is connected to the studs and hook members so that movement of the blind will cause contact of the studs with the hook members on the window frame, thereby completing the electrical circuit and generating an alarm signal. However, as can be appreciated, activation of the alarm circuit requires that the studs first be physically placed within the hook members. Further, the studs and hook members provided in the Livingston devices are not aesthetically pleasing.
In U.S. Pat. No. 3,668,582 to Lea for "Trap Switch Constructions in Normally Closed Protective Circuits of Burglar Alarm Systems", there is disclosed another type of alarm system or device for a venetian blind type flexible barrier in windows. In this patent, an alarm circuit is normally closed by means of a "trap wire" held taut across the window opening and contacting electrical contacts on either side of the opening. The circuit is such that an alarm signal is generated whenever the contact of the trap wire is broken. Normally, the trap wire is carried by the venetian blind, and consequently, movement of the blind within the opening causes the contact of the trap wire to break and an alarm signal to be generated. Accordingly, as can be appreciated, this alarm device also suffers from the same deficiency as the Livingston devices--namely, the trap wire has to be set before activation of the alarm circuit, and the trap wire and the electrical contacts on either side of the window have resulted in an unsightly appearance for the blind in the window opening.
While other types of alarm systems for window openings exist which do not result in the generation of false alarms, such systems are generally for the windows themselves and not for the flexible or movable shades or blinds. As can be appreciated, complicated restraining means for the windows are not required, nor are the windows generally susceptible to movement as a result of momentary wind disturbances and the like. For example, in U.S. Pat. Nos. 3,710,369 and 3,943,485, window alarm systems are shown in which magnets and reed switches are employed to sound an alarm upon proximity or lack of proximity of the magnets to the reed switch. Movement of the window frame, and thus movement of the magnet relative to the reed switch, is not normally free and unrestricted. Consequently, such alarm devices for windows are not generally susceptible to the same problems associated with blinds or barrier members which are normally freely movable in the window opening as a result of momentary wind disturbances and the like.